The use of fiber optics technology in data communication continues to expand at a rapid pace. Optic fiber transmission links are used widely in connecting computer, telephone, and instrumentation systems. Fiber optic systems have tremendous advantages over systems utilizing copper conductors. Besides being smaller and lighter than copper conductor systems, fiber optic systems offer total electrical isolation, extremely high speed wideband capability, and complete immunity to both noise and the broad spectrum of interference. Most importantly, fiber optic communication links are much less expensive than copper conductor systems.
A basic fiber optic communication link has three components: a transmitter, a receiver, and a fiber optic cable. The transmitter contains a light-emitting element that converts an electrical current into an optical signal. The light emitting element is typically a light-emitting diode, a laser diode, or a vertical cavity surface-emitting laser. The receiver contains a light-detecting element that converts the light signal back into an electrical current. The light-detecting element is commonly a positive-intrinsic-negative photodiode (PIN diode). The fiber optic cable connects the transmitter to the receiver and carries the optical signal between them.
More commonly, however, a fiber optic link comprises a pair of optical transceivers coupled by a pair of fiber optic cables. An optical transceiver combines a transmitter with a receiver to form a single unit that provides all required electrical/optical conversions necessary to both transmit and receive optical data. The transmitter of the first transceiver sends data in the form of an optical signal via one of the fiber optic cables to the receiver of the second transmitter which subsequently converts the optical signal to an electrical signal. Likewise, the transmitter of the second transceiver sends an optical signal via the other fiber optic cable to the receiver of the first transceiver.
One important task that must be performed by an optical transceiver module is to provide real-time monitoring and measurement of various transceiver operating conditions and parameters, and to provide these measurements to a user in a readable format. Examples of such conditions and parameters are the transceiver module operating temperature, the transceiver supply voltage, the laser biasing current, the optical input power, and the optical output power. Historically, optical transceiver modules have been constructed as “hard-coded” integrated circuits (IC's). In other words, individual circuits comprising a plurality of transistors are designed into the IC with each circuit dedicated to carrying out a single task related to the control and operation of the transceiver. Thus, one circuit is likely dedicated to monitoring and reporting each of the individual values mentioned above.
While such circuits provide for high speed transceiver module operation, they can be very complex and, thus, difficult to design and manufacture. Additionally, each circuit must be specifically designed to meet customer specific design criteria. In order to ensure that these circuits are properly designed and provide accurate data, each IC is tested after manufacture. If the IC fails to meet required design performance criteria, the IC is redesigned, re-manufactured, and re-tested unit the required design performance is met. Such an approach can be very costly and result in substantial delays in manufacturing, as each cycle can take from six to twelve months to complete. Thus, each time an IC fails to meet design requirements can result in a six to twelve month delay in delivery of the product.
Optical data systems would benefit from an optical transceiver module that can be more easily adjusted to provide more accurate monitoring and measurement of transceiver operating conditions and to meet customer specific design requirements.